The present invention relates to an intruder detection device and an intruder detection method for accurately detecting intrusion of an object (e.g., a person) into a detection area to be monitored.
In general, intruder detection devices equipped with infrared sensors, such as PIR (passive infrared) sensors, are widely popular for their high reliability.
For example, there is an intruder detection device equipped with two PIR sensors. Each of the PIR sensors is composed of a lens or mirror and pyroelectric elements, but, in most cases, the PIR sensors share the lens or mirror for the purpose of cost saving. With a slight adjustment of the positional relationship between the lens or mirror and the pyroelectric elements, detection areas of the PIR sensors are provided without a gap in a vertically or horizontally alternating arrangement.
This intruder detection device outputs a detection signal to a monitoring station when both of the PIR sensors detect an object substantially at the same time.
However, the PIR sensors may generate false alarms if temperature or light varies locally in their detection areas. Specific causes for false alarms include, among others, extraneous light from the sun or car headlights, local heat generated around an air conditioner, heater or facsimile, a small animal, such as a mouse or a pet, or a curtain at the window or a poster hanging from the ceiling which may sway with the wind.